Touch tokens (555 + 4066 + iphone)

Thread Starter


Joined Aug 5, 2011

I'm working on a project dubbed 'touch tokens'. The goal is to create small electronic devices that you can place on a capacitive touch screen, that will 'communicate' their position on the screen and their 'identity', by the frequency at which they touch the screen. This is the current prototype I've got working:

The circuit consists of a CMOS 555 in astable mode that switches a 4066. The 4066 switches a wire running from the touchscreen to one of the phone's dock connector ports.

The next stage in the project is moving the whole circuit onto the phone's screen, so I want to reduce the number of components as much as possible.

I switched from a normal NE555 to CMOS 555 already, to save power. The datasheets said I could remove the decoupling capacitor across Vdd and ground, so I did. I was wondering if for this purpose, can I also safely get rid of the bypass cap across the Voltage control (pin 5) and ground?

The 4066 is also too large for my goals, so I was planning to substitute that for a smaller single switch analog switch in DIP-8 package. Do you know any that are cheap like the 4066 and do the same thing?

Finally my biggest concern is this mandatory connection to the phone's dock connector. The phone's metal side ring also works fine, but ideally I want these things to be unconnected at all. Common sense tells me that's not possible, but maybe you know of some things I could try?

Thanks a lot!


Joined Jul 23, 2011
I never use the cap on pin 5, however I never use CMOS 555's either. I think CMOS is more susceptible to interference (correct me if I'm wrong) so it may be prerequisite.


Joined Mar 24, 2008
I don't have a clue what you are trying to accomplish, but if you want smaller go with SMT components. They are about 1/5 the size of through hole components. It is what your cell phone uses. The caps are also that small.

Thread Starter


Joined Aug 5, 2011
Ultimately SMT would be the method if these things would ever make it to production. Until then, I prefer to stick to traditional components and soldering procedures, as I don't even master that skill yet. Also, if the prototype is too large, I can't execute the ideas that I have for using these things.

Leaving aside for a while what the actual purpose is, the goal is to get a 555 astable, connected to an analog switch like the 4066 and a battery into a 1 inch cube.